Method of producing a tubular magnet

ABSTRACT

An apparatus for aligning magnetic particles in a base material formed into a substantially cylindrical member, comprising a soft magnetic core adapted to be positioned within the confines of the member, and means positioned to apply an orienting magnetic field through the walls of the member while it is positioned about said core.

United States Patent [191 Rowe et al.

[54] METHOD OF PRODUCING A TUBULAR MAGNET [76] Inventors: Robert L. Rowe, Sea Gull Hill Road, North Haven, Sag Harbor, N.Y.; Donald Peccerill, 37 Susquehanna Avenue, West Haven, Conn.

22 Filed: June 22,1970

[21] Appl. No.: $9,814

Related U.S. Application Data [62] Division of Ser. No. 684,800, Nov 21, 1967, Pat. No.

[521' U.S. Cl. ..29/608, 264/24, 264/108 [51] Int. Cl ..HOlf 3/08, HOlf 7/06 [58] Field of Search ..29/608; 264/108,

i 3,732,6i'7 1 May 15, 1973 [56] References Cited UNITED STATES PATENTS 3,387,066 6/1968 Martin et al ..264/24 3,564,705 2/1971 Cochardt ...i29/608 X 3,250,831 5/1966 Hooper ..264/24 Primary Examiner'Richard J. Herbst Assistant ExaminerCarl E. Hall Attorney- Delio and Montgomery 57 ABSTRACT An apparatus for aligning magnetic particles in a base material formed into a substantially cylindrical member, comprising a soft magnetic core adapted to be positioned within the confines of the member, and means positioned to apply an orienting magnetic field through the walls of the member while it is positioned about said core.

3 Claims, 12 Drawing Figures PATENTED RAY I 5 I975 SHEET 1 [1F 2 I METHOD OF PRODUCING A TUBULAR MAGNET This application is a division of application Ser. No. 684,800 filed Nov. 21, 1967 now US. Pat. No. 3,640,657.

This invention relates to magnets and more particularly to improvements in the manufacture of cylindrical magnets suitable for use in small motors.

Cylindrical magnets of the above-mentioned type are of a shape which conveniently fit within the housing of a small motor, so as to act as a permanent field for the motor. This is accomplished by cutting sections of the cylindrical magnet from a long length of the material and thereafter slipping the cylindrical magnet into the housing of the motor. The armature of the motor is then placed in the housing, such that it is free to rotate within the field provided by the cylindrical magnet.

In the art of cylindrical magnets, it is known that they may be produced by the utilization of an extrusion technique wherein a mixture of magnetic particles and a base carrier is processed through the extruding machine. The final step of the extruding process consists of passing the material through a special die which gives the finished material its final shape. In the past, the cylindrical magnets so produced had relatively weak field strength which appeared to be the result of random orientation of the magnetic domains embedded within the base carrier material.

In order to increase the field strength of the cylindrical magnet, applicants have provided a new and improved apparatus and method for aligning magnetic particles carried in a base material formed in the shape of a cylinder. In its broadest aspects, this invention makes use of the fact that a material provided from an extruder is generally soft and flexible, with a dough-like consistency for a short period time after exiting from the extruder. Basically, a hollow cylindrical magnet of superior characteristics is provided in the preferred embodiment of this invention by the use of means for providing a magnetic field through the walls of the cylinder while a soft magnetic core is positioned within the confines of the hollow cylinder.

In view of the foregoing, it is an object of this invention to provide a new and improved method and apparatus for manufacturing cylindrical magnets.

Another object of this invention is to provide a new and improved apparatus adapted to manufacture high field strength hollow cylindrical magnets suitable for use as the permanent field of a DC motor.

A further object of this invention is to provide a new and improved method for orienting domains of magnetic particles dispersed within a non-magnetic base material.

Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.

The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others and the apparatus embodying the features of construction, combination of elements and arrangement of parts which are adapted to effect such steps, all as exemplified in the following disclosure and the scope of the invention will be indicated in the claims.

For a fuller understanding of the invention, reference is had to the following description taken in connection with the accompanying drawings, in which:

FIG. 1 is a front view of an apparatus for preferentially orienting magnetic particles according to this invention;

FIG. 2 is a sectional view taken along line 2-2 of FIG. 1;

FIG. 3 is an enlarged view of a portion of FIG. 1;

FIG. 4 is a front view of an alternate embodiment of this invention;

FIG. 5 is a sectional view taken along line 5-5 of FIG. 4;

FIG. 6 is a top view of another embodiment of this invention, including means for forming a guide in the cylindrical magnet;

FIG. 7 is a side sectional view taken along line 77 of FIG. 6;

FIG. 8 is a side view of another embodiment according to this invention, including means for severing the wall of the cylindrical magnet;

FIG. 9 is a sectional view taken along line 9-9 of FIG. 8;

FIG. 10 is a sectional view of an extrusion die including means for forming a guide in the cylindrical magnet being extruded;

FIG. 11 is a sectional view taken along line 11-11 of FIG. 10; and

FIG. 12 is a sectional view of a further embodiment according to the invention.

Referring to FIGS. 1 3, there is illustrated a typical arrangement for making oriented extruded cylindrical magnets. The extruder die is generally shown at 9 and is preferably made of an essentially non-magnetic material such as carbide steel. In the preferred embodiment of this invention, a soft magnetic core is generally shown at 10, this core being preferably separated from the extruder by a non-magnetic material such as carbide steel, plastic, or the like, shown at lll. The core 10 is preferably of an iron material composition, such that it has good magnetic properties.

Two diametrically opposite orienting heads 12 and 13 are placed in close proximity to the die, these heads forming part of an electro-magnet, including a coil shown at 14, and adapted to be connected to a direct current source. The material to be formed into the cylindrical magnet preferably comprises anisotropic magnetic particles such as ferrites of barium, lead strontium and manganese-bismuth or iron in combination with the above. The magnetic material is in the form of small-dimensioned material and is preferably commutated or ground to ultrafme particles of the order of about 0.5 microns in diameter. The particles behave as elementary magnet units called single magnetic domains.

As a base or carrier material in which the magnetic material is mixed prior to its being placed within the extruder l5, materials such as polymers, elastomers, rubbers, plastics and other non-magnetic materials, including plasticizers as a part thereof, may be used. For ex ample, materials such as polyvinylchloride, methylmethacrylate, ureaformaldehyde, vinylacetate, vinylformaldehyde, buna N and poly ethylene may be used, as well as other non-magnetic materials not confined to plastics, such as silicon materials and other nonmagnetic metallic materials, could be used.

The magnetic particles and the non-magnetic base material are mixed together in the extruder in the normal manner and are thereafter expelled in a normal manner in a cylindrical shape, as shown at 16. In the preferred embodiment, the extruded material is in a soft state due to the heating of the material as it is being extruded (per the conventional manner of extruding). As the cylinder passes through the magnetic field, the domains are preferentially rearranged to produce anisotropy in the cylinder along the diameter AA (FIG. 3). By the use of the soft core material 11 which extends into the magnetic field, the soft core being positioned within the confines of the wall of the cylinder 16, the air gap between the magnetic heads 12 and 13 is thus minimized, resulting in a substantial improvement in orientation of the magnetic particles. Without the core, the air gap would in effect be the diameter of the extruded cylinder. With the core, the air gap is effectively reduced to the thickness of the cylinder wall. Lines of force, as provided by the magnetic heads, are shown at 17 (FIG. 3). With the use of the magnetic heads, generally shown in FIGS. 1 3, the portion of the head closest to the wall of the cylinder preferably suspends an arc of 30 to 150, accordingly the orientation preferably takes place most strongly in the portions of the cylinder also suspending an arc of about 30 to 150. Thus, there are provided preferential volumes of the cylinder between the inner and outer cylinder walls forming, in this case, a two-pole magnet and having a higher degree of orientation than the material in the two other portions of the cylinder.

Now referring to FIGS. 4 and 5, there is shown another embodiment of this invention. In place of the stationary magnetic heads 12 and 13, rotating heads 20 and 21 are provided. These rotating heads are part of an electro-magnet 22 of the type generally described with reference to FIGS. 1 3. This configuration assists in maintaining a uniform linear feed-through of the extruded cylinder. Also, if desired, the heads could be somewhat lowered to provide additional force sufficient to mechanically deform the material to further aid in the orientation of the magnetic particles within the cylinder. The cylindrical magnet of this embodiment is also shown at 16 as in FIGS. 1 3. Portions of the heads 20 and 21 which engage the outer wall of the cylinder 16 each preferably suspend an arc of about 30 to 150.

FIGS. 6 and 7 of the drawings illustrate a further embodiment of the invention, in which a member 30 in the form of a wheel is utilized and which is supported in such a manner as to form a small guide or indentation in the magnetic cylinder. The purpose of this guide is to orient the material when it is placed within the motor housing. By placing a dimple or guide in the interior of the motor housing, which cooperates with the guide 32 (FIG. 7), it is possible to insure that the orientation of the cylinder within the motor housing is correct at all times. This alleviates the necessity for testing the magnet before it is placed within the motor housing or marking the magnet so that the operator assembling the motor will place it in the housing in the correct position. The guide 32 is preferably not cut through the entire side wall, but just penetrates to a point above the inner wall of the cylinder.

With reference to FIGS. 8 and 9, there is shown another type of means for supporting the cylinder as it is being magnetized. In this embodiment, the cylindrical magnet is first spliced by a cutting wheel 35 as it comes out of the extruder. A support or mandrel 36 (preferably of soft iron, but which may also be of a nonmagnetic material) is supported by rods 39 which pass through the severed wall of the cylinder. In this manner the cylinder is supported under magnets 40.

Referring now to FIGS. 10 and 11, there is shown still another means for forming a guide or slit in the cylinder wall. In this embodiment, a portion of the die is used to support a cutting member 41 positioned at the outlet of the die, such that a guideway or slit is formed within the cylinder 42.

Referring now to FIG. 12, there is shown a further apparatus for aligning magnetic particles in a base material formed into the shape of a cylinder. Instead of the core of FIGS. 1 11, a second magnet is provided, preferably an electromagnet, shown at 50, the legs of which pass through a slit formed in the cylinder 49 produced by the cutter 35 shown in FIGS. 8 and 9 as it leaves the extruder shown at 9. Preferably, the poles of the electromagnet, shown at 51 and 52, are spaced apart by'a non-magnetic material portion 53 such as plastic, brass, etc. The poles 51 and 52 are aligned with the poles of electromagnets 56 and 57 (of the type shown in FIG. 1 or FIG. 4), such that across the cylinder walls there is provided a localized aligning field. In this manner it is possible to achieve greater effective alignment of the magnetic particles. It should also be understood that magnetic bottles or the like may be produced, using this technique, by rotating the magnets or the cylinder.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description are efficiently attained and since certain changes may be made in carrying out the above method and in the constructions set forth without departing from the spirit and scope of the invention, it is intended that all matter contained in the foregoing description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all the generic and specific features of the invention herein described and all statements of the scope of the invention which, as a matter of language, might be said to fall thercbetween.

WHAT IS CLAIMED IS:

1. A method of producing a tubular magnet which comprises:

a. extruding through a die providing a cylindrical shape a mixture comprising a non-magnetic base material and randomly oriented elemental magnets, and

b. while maintaining a magnetizable core member within the resulting cylindrical extrudate, passing the cylindrical extrudate through a plurality of rotating magnetic heads having grooves in the peripheries of said heads for engaging a portion of the outer wall of the cylindrical extrudate as said extrudate passes under said heads, said magnetic heads providing unidirectional lines of force through said extrudate, whereby said elemental magnets are oriented in the same polar direction.

2. A method according to claim 1 wherein said core member is adjacent the face of said extrusion die.

3. A method according to claim 1 wherein said core member is separated from said extrusion die by a nonmagnetic material.

I l 4' i i 

1. A method of producing a tubular magnet which comprises: a. extruding through a die providing a cylindrical shape a mixture comprising a non-magnetic base material and randomly oriented elemental magnets, and b. while maintaining a magnetizable core member within the resulting cylindrical extrudate, passing the cylindrical extrudate through a plurality of rotating magnetic heads having grooves in the peripheries of said heads for engaging a portion of the outer wall of the cylindrical extrudate as said extrudate passes under said heads, said magnetic heads providing unidirectional lines of force through said extrudate, whereby said elemental magnets are oriented in the same polar direction.
 2. A method according to claim 1 wherein said core member is adjacent the face of said extrusion die.
 3. A method according to claim 1 wherein said core member is separated from said extrusion die by a non-magnetic material. 